Indexes of diastolic RV function: load dependence and changes after chronic RV pressure overload in lambs

Abstract

Diastolic function is a major determinant of ventricular performance, especially when loading conditions are altered. We evaluated biventricular diastolic function in lambs and studied possible load dependence of diastolic parameters [minimum first derivative of pressure vs. time (dP/d t min) and time constant of isovolumic relaxation (τ)] in normal ( n = 5) and chronic right ventricular (RV) pressure-overloaded ( n = 5) hearts by using an adjustable band on the pulmonary artery (PAB). Pressure-volume relations were measured during preload reduction to obtain the end-diastolic pressure-volume relationship (EDPVR). In normal lambs, absolute dP/d t min and τ were lower in the RV than in the left ventricle whereas the chamber stiffness constant ( b) was roughly the same. After PAB, RV τ and dP/d t min were significantly higher compared with control. The RV EDPVR indicated impaired diastolic function. During acute pressure reduction, both dP/d t min and τ showed a relationship with end-systolic pressure. These relationships could explain the increased dP/d t min but not the increased τ-value after banding. Therefore, the increased τ after banding reflects intrinsic myocardial changes. We conclude that after chronic RV pressure overload, RV early relaxation is prolonged and diastolic stiffness is increased, both indicative of impaired diastolic function.